1. Field of the Invention
The present invention relates to an improvement of a multiple electron beam type flat picture image display apparatus and especially concerns the picture image display apparatus having a novel structure capable of reducing deflection voltage and obtaining high quality picture display.
2. Description of the Prior Art
Several proposals have been made on multiple electron beam type flat shaped picture display device, for example in the U.S. Pat. No. 3,935,500 (to Oess et al.) and SID 78 Digest pp. 122 to 127. Furthermore, and this is not truly prior art since it is one, the same three inventors of the present invention who have invented and proposed a multiple electron beam type picture display apparatus described in the specification of the Japanese Patent Application No. Sho 53-106788 filed on Aug. 30, 1978 (laid open as unexamined patent gazette No. Sho 55-33734 on Mar. 10, 1980) and also described in the specification of the U.S. Pat. No. 4,227,117 (to Watanabe et al.) patented on Oct. 7, 1980.
The structure of picture image display apparatus of the abovementioned described invention is shown in FIG. 1(a) which is an exploded view of the principal part of the apparatus. The apparatus comprises, as shown from the upper part to the lower part in FIG. 1(a), and FIG. 1(b), an isolation electrode 2 having a plural number of isolation walls 201 to define oblong isolated spaces 202, a row of predetermined number M (e.g. M=15) of linear thermionic cathodes 1 disposed in parallel (i.e., line cathodes, each of which comprises a linear filament line to be heated by a low voltage, e.g., D.C. 10 V and electron emissive oxide coating thereon, and hereinafter is referred to as linear thermionic cathode) each being disposed in the isolated spaces 202, an extractor electrode 3 having a predetermined number N (e.g. N=107) of electron beam passing apertures 3a disposed in rows below the linear thermionic cathodes 1, a row of control electrodes 4 for controlling beam intensity disposed parallelly in a direction perpendicular to those of said linear thermionic cathodes 1 each having electron beam passing openings 4a below the apertures 3a, an electron beam forming electrode 5 having electron beam passing openings 5a below the openings 4a, a row of vertical deflection electrodes comprising pairs of common-connected first electrodes 6 and common-connected second electrodes 6', a row of horizontal deflection electrodes comprising pairs of common-connected first electrodes 7 and common-connected second electrodes 7', and electric field shielding electrode 8, and anode 9 of vapor-deposited thin aluminum film, and a phosphor screen 10 formed on a face panel 11 of a vacuum enclosure and under said anode 9. Every electron beam e, e . . . passes through deflection spaces 62, 62 . . . and 72, 72 . . . defined by the deflection electrodes pairs 6, 6' . . . and 7, 7' . . . disposed regularly in the same order with respect to every electron beam as shown in FIG. 1(a) and FIG. 1(b).
In the operation of such multiple electron beam type display apparatus described in the abovementioned specifications, scannings of beam spots on the phosphor screen are made in the known line-at-a-time type scanning, wherein ordinary time-sequential image signal is converted into a plural number of parallel signals. For example, by taking a case to display an image field raster having numbers of picture elements of 240 (in vertical direction) times 321 (in horizontal direction), with regard to the horizontal scanning of the beam spots the raster is divided into a plural number N of vertically oblong sections, wherein the horizontal scannings are carried out simultaneously in all of N sections. Then, each section has picture elements of n=(321/N) in the horizontal direction. For example, when the number N of the vertical sections is 107, the number n of picture elements in each section is 3. For such example, 107 beam spots are produced from each linear thermionic cathode and 107 control electrodes are provided in order to control the 107 electron beam intensities. In the apparatus, the horizontal scanning is made by using sawtooth wave having a horizontal scanning period H applied to the horizontal deflection electrode and in a manner that all the N beam spots are deflected simultaneously to scan in the same direction taking one horizontal scanning period H. The horizontal scanning period H is equal to the horizontal scanning period of the ordinary time sequential television signal. In order for attaining such line-at-a-time-scanning, the ordinary time sequential image signal is preliminarily converted into the N parallel signals of the line-at-a-time type.
The vertical scanning of the described apparatus is made by dividing the raster into a plural number M of horizontally oblong sections, and at first in the first section, for example in the uppermost section, the plural number of beam spots, which simultaneously scan, also scan vertically (downwards). When the vertical scanning in the first section is over and all the beam spots reach the bottoms of the first horizontally oblong sections, then the forming of electron beams from the electron from the first linear thermionic cathode ends and the forming of electron beams from the electrons from the second linear thermionic cathode starts, and the vertical scannings of the beam spots start in the second horizontally oblong section and scan downwards in the same way as in the first section. The vertical scanning is made thus downwards to the bottom or M-th section by applying a saw-tooth wave having a period V/M, where V is the vertical scanning period of the ordinary television signal. For the abovementioned example of the raster having the number of vertical picture element of 240, when the number M of the horizontally oblong sections is 15, each of the section has the horizontal scanning lines of a number of m=(240/15)=16. That is to say, the example apparatus uses 15 linear thermionic cathodes, and each cathode vertically scans to produce 16 horizontal scanning lines.
FIG. 1(c) shows a block diagram of an example of the circuit for driving the abovementioned apparatus described in the abovementioned specifications. The circuit of FIG. 1(c) is constituted as follows. A video signal from the input terminal 12 is led to a video signal amplifier 13 and a synchronization signal separator 14, output of which is given to a sampling pulse generator 15 and a synchronization signal generator 19. A memory circuit 16 receives time sequential signal from the video amplifier 13 and sample-hold it in order for conversion it to the parallel type video signal by a multiplexer 17. That is, the multiplexer 17 takes out memorized video signal from the memory 16 and rearranges it into the N (=107) parallel signals, in each of which n (=3) data in the memory 16 are rearranged into time sequential signal to take the time period of H. The parallel outputs of the multiplexer 17 are given through an amplifier 18 to the control electrodes of the display apparatus. Horizontal deflection signal generator 20 and vertical deflection signal generator 22 receive signal from the synchronization signal generator 19 and issue horizontal deflection signal and vertical deflection signal through the amplifiers 21 and 23 to the horizontal deflection electrodes and vertical deflection electrodes of the display apparatus, respectively. A cathode control circuit 24 receives signal from the synchronization signal generator 19 and issues control signal to the linear thermionic cathodes, in order that electron beams are selectively formed from the electrons from a selected one of linear thermionic cathodes in sequence by application of negative potential thereto with respect to the electrode 3, thereby to scan for the period of m.times.H.
FIG. 1(d) shows waveforms (A), (B), (C), (D), (E), (F), and (G) of various parts of FIG. 1(c) circuit for the example of n=3 and m=16. The waveforms (A) and (B) are those of horizontal synchronization signal and vertical synchronization signal, wherein H designates the time period of one horizontal scanning and V designates the time period of one vertical scanning of the ordinary television signal. The waveforms (C) and (D) are voltages to be applied to the first and the second linear thermionic cathodes, respectively for switchingly operating the cathode in sequence. The waveforms (E) and (F) are issued from the vertical deflection signal generator circuit 22 and horizontal deflection signal generator circuit 20, respectively, and the waveform (G) is the control signal to be applied to the control electrode 4 of the display apparatus. Accordingly, the scannings of the beam spots seen at an enlarged part of the phosphor screen is as shown in FIG. 1(e).
In the picture display apparatus elucidated referring to FIG. 1(a) and FIG. 1(b), the electric field shielding electrode 8 is provided and a positive potential of several hundred volts against the horizontal deflection electrodes 7, 7' is impressed thereon. This electric field shielding electrode 8 serves to limit deflection angles of the electron beams by means of selecting sizes and positional relations of its square shaped openings with respect to paths of electron beams, and therefore, its apperture pattern must be very accurate. Accordingly, the electric field shielding electrode 8 is made lithographic process and hence its thickness is thin, and furthermore, in order to attain a high aperture ratio for high electron beams transmission its aperture size is large remaining very fine ribs inbetween. Such a thin electrode having very fine ribs has a difficulty in rigidity against shock or vibration and in stability of registration. Furthermore, by means of a high electric field at the electron 8, there has been a problem that the electron beam deflection is distorted when deflection angle is large, and removing of such distortion of deflection requires an increase of the voltage for deflection of the signal. The picture display apparatus of FIG. 1(a) and FIG. 1(b) has another problem that its deflection electrodes of thin parallel wire structure is likely to form sags or pattern distortions by means of thermal stress due to, for instance, a high temperature at its glass frit fixing, and such sags or pattern distortions leads to eventual nonuniformity or deflection angle at parts on the picture screen and hence to undesirable white or black lines on the reproduced picture due to overlapping of neighboring scanning lines or undue gap between the neighboring scanning lines.